Silicon-carbon composite material, preparation method and application

Abstract

The invention relates to the technical field of preparation of battery negative electrode materials, and discloses a silicon-carbon composite material, a preparation method and application, and the preparation method of the silicon-carbon composite material comprises the following steps: obtaining porous carbon; the soft carbon precursor and the porous carbon are mixed and coated in a solvent to obtain the porous carbon with a coating layer, the solvent is a non-polar or weak-polar solvent, and the molecular diameter MD of the soft carbon precursor is larger than 5 nm; coating layer carbonization: performing high-temperature heat treatment on the porous carbon with the coating layer in an inert atmosphere to obtain carbonized porous carbon; and silicon-carbon compounding: carrying out silicon source deposition on the carbonized porous carbon to obtain the silicon-carbon composite material. According to the invention, the silicon-carbon composite material with a lower proportion of nano silicon deposited on the outer surface of porous carbon can be prepared, and the cycle and storage performance of the battery can be effectively improved.

Description

Technical Field

[0001] This application relates to the field of battery anode material technology, specifically to a silicon-carbon composite material, its preparation method, and its application. Background Technology

[0002] For lithium-ion silicon-carbon anode materials prepared by CVD, during the deposition reaction, the surface defects of porous carbon catalyze the deposition of nano-silicon generated from silane decomposition onto the inner / outer surfaces of the porous carbon. Due to the confinement of the pore space, the nano-silicon grains deposited within the micropores are relatively small, and the encapsulated carbon matrix effectively buffers the volume changes of silicon particles during lithium insertion / extraction. However, when nano-silicon is deposited on the outer surface of the porous carbon (particle surface or macroporous / macroporous surface), the confinement effect of the carbon matrix weakens or even disappears. Simultaneously, the nano-silicon grains are larger and prone to crystallization. The unconstrained volume changes of these silicon particles during charge and discharge lead to particle pulverization and peeling, resulting in repeated rupture and regeneration of the SEI film. Especially when the proportion of nano-silicon deposited on the outer surface of the porous carbon is high, it significantly degrades the cycle and storage performance of batteries prepared using this silicon-carbon anode material. Summary of the Invention

[0003] This application provides a silicon-carbon composite material to solve the problem that the cycling and storage performance deteriorates when the proportion of nano-silicon deposited on the porous carbon outer surface is too high in the existing lithium-ion battery silicon-carbon anode materials prepared by CVD method. This allows for the preparation of silicon-carbon composite materials with a lower proportion of nano-silicon deposited on the porous carbon outer surface, thereby improving the cycling and storage performance of the battery.

[0004] In a first aspect, this application provides a method for preparing a silicon-carbon composite material, comprising: Obtaining porous carbon; Porous carbon modification: A soft carbon precursor is mixed with porous carbon in a solvent to obtain porous carbon with a coating layer. The solvent is a nonpolar or weakly polar solvent, and the molecular diameter MD of the soft carbon precursor is >5 nm. Carbonization of the coating layer: Porous carbon with a coating layer is heat-treated under an inert atmosphere to obtain carbonized porous carbon; Silicon-carbon composite: Silicon-carbon composite material is obtained by depositing silicon source on carbonized porous carbon.

[0005] In one alternative implementation, 5 nm < molecular diameter MD of the soft carbon precursor ≤ 200 nm; And / or, the mass of the soft carbon precursor is 5%-15% of the mass of the porous carbon.

[0006] And / or, the specific surface area of ​​the porous carbon is 1500-2500 m². 2 / g, pore volume 0.6-1.2cm3 / g; And / or, the porous carbon is biomass-based porous carbon, including one or more of coconut shell charcoal, bamboo charcoal or rice husk charcoal; And / or, the solvent includes one or more of toluene, hexane, and tetrahydrofuran; And / or, the soft carbon precursor includes one or more of aqueous asphalt emulsions, polyvinyl chloride, polyacrylonitrile, chitosan, or starch derivatives.

[0007] In one optional embodiment, the soft carbon precursor and the porous carbon are respectively mixed with a solvent to prepare a soft carbon precursor solution and a porous carbon dispersion, and then the soft carbon precursor solution and the porous carbon dispersion are mixed and coated.

[0008] In one optional embodiment, in the step of carbonizing the coating layer, the gas in the inert atmosphere is nitrogen or argon, the temperature of the heat treatment is 800℃-2000℃, and the heat treatment time is 1-4h.

[0009] In one optional embodiment, the silicon source for silicon source deposition is silane, and the silicon source deposition temperature is 400℃-600℃.

[0010] In one optional embodiment, the silicon source deposition step is followed by carbon source vapor deposition, wherein the carbon source used in the carbon source vapor deposition is acetylene, methane or ethylene, and the deposition temperature is 400℃-600℃.

[0011] In one optional embodiment, the silicon-carbon composite material is placed in a 0.1M alkaline solution of potassium hydroxide or sodium hydroxide, and the gas production per unit mass G is less than 10 ml / mg over 24 hours.

[0012] Secondly, this application provides a silicon-carbon composite material prepared by the above-described preparation method.

[0013] Thirdly, this application provides a secondary battery comprising the aforementioned silicon-carbon composite material.

[0014] Fourthly, this application also provides an application of silicon-carbon composite materials in negative electrode sheets, secondary batteries, and electrical equipment.

[0015] The technical solution of this application has the following advantages: 1. The silicon-carbon composite material provided in this application is obtained by coating porous carbon with a soft carbon precursor solution, followed by conventional heat treatment and silicon deposition. The soft carbon precursor solution uses a molecular diameter MD > 5 nm and a non-polar or weakly polar solvent. The high molecular weight soft carbon precursor is synergistically coated on the surface of porous carbon by the non-polar or weakly polar solvent. The selection of a carbon precursor with a molecular diameter > 5 nm utilizes the steric hindrance effect of its large molecular structure to make it difficult for it to enter the smaller micropores of porous carbon. At the same time, the use of a non-polar or weakly polar solvent with low dielectric constant and low surface tension can weaken the interaction between the solvent and the polar functional groups on the surface of porous carbon, further promoting the selective adsorption of the coating agent on the mesopores / macropores and the outer surface, and reducing surface defects in this part. Therefore, the combination of the two can greatly reduce the defect density of the mesopores and macropores of porous carbon particles, thereby reducing the deposition in the reaction area, reducing the proportion of surface silicon, improving the problem of floating silicon, and thus improving the overall cycle and storage life of the silicon-carbon anode material. Meanwhile, the heat-treated soft carbon precursor pyrolyzes on the porous carbon surface to generate a dense and continuous coated carbon layer. This coated layer provides mechanical buffer and constraint for the small amount of silicon that may be deposited on or near it, effectively suppressing its volume expansion and reducing the direct contact area between silicon and electrolyte, significantly reducing side reactions and promoting the formation of a thinner and more stable SEI film.

[0016] 2. The silicon-carbon composite material provided in this application adopts the standard of gas production G < 10 ml / mg. Since the highly active "silicon-rich" surface will react violently with alkaline solution to produce hydrogen gas, the introduction of this standard can directly, quickly and quantitatively reflect the content of highly active silicon surface in the material. This proves that the present invention can effectively reduce the content of highly active silicon on the surface. The cycle life and storage performance of the material can be accurately predicted through offline testing, ensuring the consistency and reliability of the product. Attached Figure Description

[0017] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 This is an electron microscope image of the surface-modified silicon-carbon particles in Example 1 of this invention. Detailed Implementation The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion. In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0020] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0021] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0022] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces). In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0023] To address the problems existing in the aforementioned related technologies, according to a first aspect of this application, a method for preparing a silicon-carbon composite material is provided, comprising: obtaining porous carbon; modifying porous carbon: mixing and coating a soft carbon precursor with porous carbon in a solvent to obtain porous carbon with a coating layer, wherein the solvent is a non-polar or weakly polar solvent, and the molecular diameter MD of the soft carbon precursor is >5 nm; carbonizing the coating layer: heat-treating the porous carbon with the coating layer under an inert atmosphere to obtain carbonized porous carbon; and silicon-carbon composite: depositing a silicon source on the carbonized porous carbon to obtain a silicon-carbon composite material.

[0024] The method for detecting the molecular diameter (MD) of soft carbon precursors is as follows: dynamic light scattering method is used to test the hydrodynamic size of nanoparticles or polymers in solution. Commonly used test parameters are scattering angle: 90°, laser wavelength: 658nm.

[0025] The silicon-carbon composite material provided in this application is obtained by coating porous carbon with a soft carbon precursor solution, followed by conventional heat treatment and silicon deposition. The soft carbon precursor solution uses a molecular diameter (MD) > 5 nm and a non-polar or weakly polar solvent. The high molecular weight soft carbon precursor is synergistically coated onto the porous carbon surface by the non-polar or weakly polar solvent. The selection of a carbon precursor with a molecular diameter > 5 nm utilizes the steric hindrance effect of its large molecular structure, making it difficult for it to enter the smaller micropores of the porous carbon. Simultaneously, the use of a non-polar or weakly polar solvent with low dielectric constant and low surface tension weakens the interaction between the solvent and the polar functional groups on the porous carbon surface, further promoting the selective adsorption of the coating agent on the mesopores / macropores and the outer surface, reducing surface defects in this area. Therefore, the combined effect of these two factors can significantly reduce the defect density on the mesopores and macropores of the porous carbon particles, thereby reducing deposition in the reaction region, lowering the proportion of surface silicon, improving the silicon floating problem, and thus improving the overall cycle and storage life of the silicon-carbon anode material. Meanwhile, the heat-treated soft carbon precursor pyrolyzes on the porous carbon surface to generate a dense and continuous coated carbon layer. This coated layer provides mechanical buffer and constraint for the small amount of silicon that may be deposited on or near it, effectively suppressing its volume expansion and reducing the direct contact area between silicon and electrolyte, significantly reducing side reactions and promoting the formation of a thinner and more stable SEI film.

[0026] In one optional embodiment, 5nm < molecular diameter MD of the soft carbon precursor ≤ 200nm; when the molecular diameter MD of the soft carbon precursor of this application is too large, it may block the pores of the porous carbon, resulting in a decrease in silicon carrying capacity and a lower capacity of the silicon-carbon material; when the molecular diameter is too small, the soft carbon molecules will diffuse into the pores of the porous carbon, which will also cause a decrease in the pore volume of the matrix.

[0027] In one optional embodiment, the mass amount of the soft carbon precursor is 5%-15% of the porous carbon mass, for example: the mass amount of the soft carbon precursor is 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% of the porous carbon mass, etc.; if the amount of soft carbon precursor used in this application is too large, it will affect the overall capacity of the material; if the amount of soft carbon precursor used is too small, it cannot play an effective improvement role.

[0028] In one optional embodiment, the porous carbon has a specific surface area of ​​1500-2500 m². 2 / g, pore volume 0.6-1.2cm 3 / g. For example: the specific surface area of ​​porous carbon is 1500m². 2 / g, 1600m 2 / g、1700m 2 / g、1800m 2 / g、1900m 2 / g、2000m 2 / g、2100m 2 / g、2200m 2 / g、2300m 2 / g、2400m 2 / g、2500m 2 / g etc.; If the specific surface area and pore volume of the porous carbon in this application are too low, the silicon-bearing capacity will be weak, and the capacity of the silicon-carbon material produced will be low; if the specific surface area and pore volume of the porous carbon are too high, it will affect the strength of the carbon matrix, causing the silicon-carbon material to break into particles after rolling, resulting in a low initial efficiency.

[0029] The specific surface area of ​​porous carbon in this application is determined by the nitrogen adsorption-desorption isotherm method (BET method). The pore volume of porous carbon in this application is determined by estimating the total pore volume based on the nitrogen adsorption-desorption isotherm method by analyzing the maximum amount of nitrogen adsorbed in the adsorption curve. Typically, the adsorption amount at a relative pressure close to 1 is converted to the volume in liquid nitrogen, which is then considered the total pore volume (unit: cm³ / g).

[0030] In one optional embodiment, the porous carbon is biomass-based porous carbon, including one or more of coconut shell charcoal, bamboo charcoal, or rice husk charcoal. And / or, the solvent includes one or more of toluene, hexane, and tetrahydrofuran; And / or, the soft carbon precursor includes one or more of aqueous asphalt emulsions, polyvinyl chloride, polyacrylonitrile, chitosan, or starch derivatives.

[0031] In one optional embodiment, during the carbonization step of the coating layer, the inert atmosphere contains nitrogen or argon, the heat treatment temperature is 800℃-2000℃, and the heat treatment time is 1-4 hours. For example, the heat treatment temperature can be 800℃, 900℃, 1000℃, 1100℃, 1200℃, 300℃, 1400℃, 1500℃, 1600℃, 1700℃, 1800℃, 1900℃, 2000℃, or any range thereof, and the heat treatment time can be 1 hour, 2 hours, 3 hours, 4 hours, or any range thereof. In this application, if the heat treatment temperature is too low, the carbonization of the soft carbon precursor is incomplete, resulting in a low rate of ion and electron transport in the matrix; if the heat treatment temperature is too high, the original abundant pores will form closed pores, reducing the silicon-bearing capacity. If the heat treatment time is too short, incomplete carbonization will occur; if the heat treatment time is too long, overheating will occur, resulting in more closed pores. Therefore, suitable heat treatment conditions can be selected by comprehensively adjusting the time and temperature.

[0032] In one optional embodiment, the silicon source for silicon source deposition is silane, and the silicon source deposition temperature is 400℃-600℃. For example, the silicon source deposition temperature can be 400℃, 450℃, 500℃, 550℃, 600℃, or within any range of the above values. If the silicon source deposition temperature is too low, the silane cannot decompose and deposit; if the silicon source deposition temperature is too high, the silicon particles are prone to crystallization, resulting in poor cycling performance of the silicon-carbon material.

[0033] In one optional embodiment, the silicon source deposition step is followed by carbon source vapor deposition, wherein the carbon source used in the carbon source vapor deposition is acetylene, methane, or ethylene, and the deposition temperature is 400℃-600℃. For example, the carbon source vapor deposition temperature can be 400℃, 450℃, 500℃, 550℃, 600℃, or any range of the above values. If the carbon source vapor deposition temperature is too low, acetylene cannot decompose and deposit; if the carbon source vapor deposition temperature is too high, silicon carbon will react with silicon carbide at the higher temperature, causing material deactivation.

[0034] In one optional embodiment, the silicon-carbon composite material is placed in a 0.1M alkaline solution of potassium hydroxide or sodium hydroxide, and the gas production per unit mass G is less than 10 ml / mg over 24 hours.

[0035] Since highly active "silicon-rich" surfaces react violently with alkaline solutions to produce hydrogen gas, this application introduces a standard of hydrogen production rate G < 10 ml / mg. This standard directly, quickly, and quantitatively reflects the content of highly active silicon surfaces in the material. The lower the content of highly active silicon surfaces, the better the cycle life and storage performance of the battery prepared from it. This standard can indirectly prove that silicon-carbon composite materials with a content of highly active silicon below this standard have a lower content of silicon on the surface, resulting in a battery with better cycle life and storage performance. In other words, by setting this standard, even through offline testing, the cycle life and storage performance of the material can be accurately predicted indirectly, ensuring the consistency and reliability of the product.

[0036] Secondly, this application provides a silicon-carbon composite material prepared by the above-described preparation method.

[0037] Thirdly, this application provides a secondary battery comprising the aforementioned silicon-carbon composite material.

[0038] Fourthly, this application also provides an application of silicon-carbon composite materials in negative electrode sheets, secondary batteries, and electrical equipment.

[0039] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0040] Example 1 A silicon-carbon compound comprising: 1) Carrier preparation: Take 1000g of biomass-based porous carbon (coconut shell carbon), with a specific surface area of ​​1950m² / g, a pore volume of 0.9cm³ / g, and an average pore diameter of 1.85nm. Vacuum dry it at 120℃ for 12 hours to remove water. 2) Selective liquid-phase coating: a. Disperse the above-mentioned dried porous carbon in 10L of toluene solvent and sonicate for 30 minutes to ensure full dispersion; b. Slowly add 200g of aqueous asphalt emulsion with a solid content of 50% (asphalt molecule size approximately 10-50 nm) under vigorous stirring; c. After addition, continue stirring at 60℃ for 6 hours to allow asphalt molecules to selectively adsorb onto the mesopores / macropores and outer surface of the porous carbon through steric hindrance and the low polarity of the solvent; d. Separate the solid by vacuum filtration and wash three times with fresh toluene to remove the surface-physically adsorbed coating agent. 3) Heat treatment: The washed sample was placed in a box furnace and heated to 1300℃ at a rate of 5℃ / min under argon protection, and held at that temperature for 2 hours. After natural cooling, a surface-modified porous carbon support (denoted as C@PC) was obtained.

[0041] 4) Silicon-Carbon Composite: a. Silane Deposition: The C@PC support was placed in a chemical vapor deposition (CVD) furnace, and a mixture of silane (SiH4) and argon (volume ratio 1:9) was introduced at 500°C for 300 minutes; b. Acetylene Deposition: Subsequently, without changing the temperature, the silane was turned off, and acetylene (C2H2) gas was introduced for 120 minutes to achieve carbon coating. After the reaction, the mixture was cooled to room temperature under an argon atmosphere to obtain the final silicon-carbon composite. The electron micrograph of the silicon-carbon composite is shown below. Figure 1 As shown.

[0042] Example 2 A silicon-carbon compound comprising: 1) Carrier preparation: Take 1000g of biomass-based porous carbon (coconut shell carbon), with a specific surface area of ​​1950m² / g, a pore volume of 0.9cm³ / g, and an average pore diameter of 1.85nm. Vacuum dry it at 120℃ for 12 hours to remove water. 2) Selective liquid-phase coating: a. Disperse the above-mentioned dried porous carbon in 10 L of tetrahydrofuran (THF) and sonicate for 30 minutes to ensure full dispersion; b. Slowly add THF containing 100 g of polyvinyl chloride (polyvinyl chloride with a molecular weight of less than 100,000 g / mol and a molecular size of 5 nm < 10 nm) under vigorous stirring; c. After addition, continue stirring at 60 °C for 6 hours to allow polyvinyl chloride to selectively adsorb onto the mesopores / macropores and outer surface of the porous carbon through steric hindrance and the low polarity of the solvent; d. Separate the solid by vacuum filtration and wash three times with fresh toluene to remove the surface-physically adsorbed coating agent. 3) Heat treatment: The washed sample was placed in a box furnace and heated to 1300℃ at a rate of 5℃ / min under argon protection, and held at that temperature for 2 hours. After natural cooling, a surface-modified porous carbon support (denoted as C@PC) was obtained.

[0043] 4) Silicon-Carbon Composite: a. Silane Deposition: The C@PC support is placed in a chemical vapor deposition (CVD) furnace, and a mixture of silane (SiH4) and argon (volume ratio 1:9) is introduced at 500°C for 300 minutes; b. Acetylene Deposition: Subsequently, without changing the temperature, the silane is turned off, and acetylene (C2H2) gas is introduced for 120 minutes to achieve carbon coating. After the reaction is completed, the mixture is cooled to room temperature under an argon atmosphere to obtain the final silicon-carbon composite.

[0044] Example 3 A type of silicon-carbon, differing from Example 1 in that the biomass-based porous carbon is made from rice husk charcoal, and has a specific surface area of ​​1500 m². 2 / g, pore volume 0.6cm 3 / g; other conditions are the same as in Example 1.

[0045] Example 4 A type of silicon-carbon, differing from Example 1 in that the biomass-based porous carbon is made from bamboo charcoal, and has a specific surface area of ​​2500 m². 2 / g, pore volume 1.2cm 3 / g; other conditions are the same as in Example 1.

[0046] Example 5 A silicon-carbon compound differs from Example 1 in that, in the porous carbon modification step, hexane is used instead of toluene as the solvent, and a 50% chitosan-hexane solution (10nm < molecular size < 100nm) is used instead of an aqueous asphalt emulsion with a solid content of 50%; other conditions are the same as in Example 1.

[0047] Example 6 A silicon-carbon compound differs from Example 1 in that, in the porous carbon modification step, a 50% mass concentration polyacrylonitrile-toluene solution (10nm < polyacrylonitrile molecular size < 30nm) replaces the 50% solid content aqueous asphalt emulsion; other conditions are the same as in Example 1.

[0048] Example 7 A silicon-carbon compound differs from Example 1 in that, in the porous carbon modification step, hexane is used instead of toluene as the solvent, and a starch derivative-toluene solution with a mass concentration of 50% (starch derivative molecular size 50-200nm) is used instead of an aqueous asphalt emulsion with a solid content of 50%; other conditions are the same as in Example 1.

[0049] Example 8 A silicon-carbon alloy, differing from Example 1 in that the heat treatment temperature is 800°C and the heat treatment time is 4 hours, while other conditions are the same as in Example 1.

[0050] Example 9 A silicon-carbon alloy, differing from Example 1 in that the heat treatment temperature is 2000°C and the heat treatment time is 1 hour, while other conditions are the same as in Example 1.

[0051] Example 10 A silicon-carbon alloy, differing from Example 1 in that the silicon source is deposited at a temperature of 400°C. The carbon source vapor deposition is also performed at 400°C, with other conditions identical to Example 1.

[0052] Example 11 A silicon-carbon alloy, differing from Example 1 in that the silicon source is deposited at a temperature of 600°C. The carbon source vapor deposition is also performed at 600°C, with other conditions identical to Example 1.

[0053] Example 12 A silicon-carbon method, differing from Example 1 in that the carbon source used in the carbon source vapor deposition is methane, while other conditions are the same as in Example 1.

[0054] Example 13 A silicon-carbon method, differing from Example 1 in that the carbon source vapor deposition uses ethylene as the carbon source, while other conditions are the same as in Example 1.

[0055] Example 14 A silicon-carbon precursor, differing from Example 1 in that the amount of the soft carbon precursor used is 5% of the porous carbon mass, while other conditions are the same as in Example 1.

[0056] Example 15 A silicon-carbon precursor, differing from Example 1 in that the amount of the soft carbon precursor used is 15% of the porous carbon mass, while other conditions are the same as in Example 1.

[0057] Comparative Example 1 A silicon-carbon compound comprising: 1) Carrier preparation: Take 1000g of biomass-based porous carbon (coconut shell carbon), with a specific surface area of ​​1950m² / g, a pore volume of 0.9cm³ / g, and an average pore diameter of 1.85nm. Vacuum dry it at 120℃ for 12 hours to remove water. 2) Silicon-Carbon Composite: a. Silane Deposition: Porous carbon is placed in a chemical vapor deposition (CVD) furnace, and a mixture of silane (SiH4) and argon (volume ratio 1:9) is introduced at 500°C for 300 minutes; b. Acetylene Deposition: Subsequently, without changing the temperature, the silane is turned off, and acetylene (C2H2) gas is introduced for 120 minutes to achieve carbon coating. After the reaction is completed, the mixture is cooled to room temperature under an argon atmosphere to obtain the final silicon-carbon composite.

[0058] Comparative Example 2 A silicon-carbon compound comprising: 1) Carrier preparation: Take 1000g of biomass-based porous carbon (coconut shell carbon), with a specific surface area of ​​1950m² / g, a pore volume of 0.9cm³ / g, and an average pore diameter of 1.85nm. Vacuum dry it at 120℃ for 12 hours to remove water. 2) Selective liquid phase coating: a. Disperse the above-mentioned dried porous carbon in 10L of ethanol solvent and sonicate for 30 minutes to ensure full dispersion; b. Slowly add 100g of sucrose (molecular size <2 nm) under vigorous stirring; c. After addition, continue stirring at 60℃ for 6 hours; d. Evaporate the solvent. 3) Heat treatment: The washed sample was placed in a box furnace and heated to 1300℃ at a rate of 5℃ / min under argon protection, and held at that temperature for 2 hours. After natural cooling, a surface-modified porous carbon support (denoted as C@PC) was obtained.

[0059] 4) Silicon-Carbon Composite: a. Silane Deposition: The C@PC support is placed in a chemical vapor deposition (CVD) furnace, and a mixture of silane (SiH4) and argon (volume ratio 1:9) is introduced at 500°C for 300 minutes; b. Acetylene Deposition: Subsequently, without changing the temperature, the silane is turned off, and acetylene (C2H2) gas is introduced for 120 minutes to achieve carbon coating. After the reaction is completed, the mixture is cooled to room temperature under an argon atmosphere to obtain the final silicon-carbon composite.

[0060] Comparative Example 3 A silicon-carbon compound comprising: 1) Carrier preparation: Take 1000g of biomass-based porous carbon (e.g., coconut shell charcoal), with a specific surface area of ​​1950m² / g, a pore volume of 0.9cm³ / g, and an average pore diameter of 1.85nm, and vacuum dry it at 120℃ for 12 hours to remove water. 2) Selective liquid-phase coating: a. Disperse the above-mentioned dried porous carbon in 10L of ethanol solvent and sonicate for 30 minutes to ensure full dispersion; b. Slowly add 200g of aqueous asphalt emulsion with a solid content of 50% (asphalt molecule size approximately 10-50 nm) under vigorous stirring; c. After addition, continue stirring at 60℃ for 6 hours to allow asphalt molecules to selectively adsorb onto the mesopores / macropores and outer surface of the porous carbon through steric hindrance and the low polarity of the solvent; d. Separate the solid by vacuum filtration and wash three times with fresh toluene to remove the surface-physically adsorbed coating agent. 3) Heat treatment: The washed sample was placed in a box furnace and heated to 1300℃ at a rate of 5℃ / min under argon protection, and held at that temperature for 2 hours. After natural cooling, a surface-modified porous carbon support (denoted as C@PC) was obtained.

[0061] 4) Silicon-Carbon Composite: a. Silane Deposition: The C@PC support is placed in a chemical vapor deposition (CVD) furnace, and a mixture of silane (SiH4) and argon (volume ratio 1:9) is introduced at 500°C for 300 minutes; b. Acetylene Deposition: Subsequently, without changing the temperature, the silane is turned off, and acetylene (C2H2) gas is introduced for 120 minutes to achieve carbon coating. After the reaction is completed, the mixture is cooled to room temperature under an argon atmosphere to obtain the final silicon-carbon composite.

[0062] Comparative Example 4 A silicon-carbon compound comprising: 1) Carrier preparation: Take 1000g of biomass-based porous carbon (coconut shell carbon), with a specific surface area of ​​2000m² / g, a pore volume of 0.9cm³ / g, and an average pore diameter of 1.9nm. Vacuum dry it at 120℃ for 12 hours to remove water. 2) Selective liquid-phase coating: a. Disperse the above-mentioned dried porous carbon in 10 L of toluene solvent and sonicate for 30 minutes to ensure full dispersion; b. Slowly add 100 g of sucrose (molecular size <2 nm) under vigorous stirring; c. After the addition is complete, continue stirring at 60 °C for 6 hours; d. Separate the solid by vacuum filtration and wash it three times with fresh toluene to remove the coating agent physically adsorbed on the surface. 3) Heat treatment: The washed sample was placed in a box furnace and heated to 1300℃ at a rate of 5℃ / min under argon protection, and held at that temperature for 2 hours. After natural cooling, a surface-modified porous carbon support (denoted as C@PC) was obtained.

[0063] 4) Silicon-Carbon Composite: a. Silane Deposition: The C@PC support is placed in a chemical vapor deposition (CVD) furnace, and a mixture of silane (SiH4) and argon (volume ratio 1:9) is introduced at 500°C for 300 minutes; b. Acetylene Deposition: Subsequently, without changing the temperature, the silane is turned off, and acetylene (C2H2) gas is introduced for 120 minutes to achieve carbon coating. After the reaction is completed, the mixture is cooled to room temperature under an argon atmosphere to obtain the final silicon-carbon composite.

[0064] Experimental Example 1. Gas production per unit mass test: The obtained silicon-carbon composite material was placed in a 0.1M sodium hydroxide solution in a constant temperature test room at 25℃ for testing. The gas production per unit mass was counted over 24 hours. The material was deemed qualified if the gas production per unit mass G < 10 ml / mg.

[0065] 2. Silicon Content Detection: The silicon-carbon materials obtained in the examples and comparative examples were placed in an air atmosphere and gradually heated to 1100℃ at a rate of 5℃ / min. During this process, the carbon will completely react to generate carbon dioxide and evaporate, while the silicon will react with oxygen to generate silicon dioxide. Finally, the silicon content in the original silicon-carbon composite material was calculated based on the mass of silicon dioxide generated.

[0066] 3. Obtain the electrochemical performance of the negative electrodes prepared from silicon-carbon in each embodiment and comparative example, assembled into CR2032 coin cell half-cells and full cells.

[0067] The assembly process of CR2032 coin cell half-cell or full cell is as follows: Silicon carbon is used as the negative electrode material, and a negative electrode active slurry is prepared by mixing it with a solvent in a ratio of negative electrode material: binder SBR: conductive agent SP: dispersant CMC = 9:0.4:0.15:0.45. The negative electrode active slurry is then coated onto a current collector to form a negative electrode sheet. Lithium cobalt oxide is used as the positive electrode sheet, and an electrolyte (1M LiPF6, EC / DEC / DMC = 1:1:1) is added. The cells are then assembled into CR2032 coin cell half-cells and full cells in a vacuum glove box. The capacity and first efficiency of CR2032 coin cell half-cells were tested, and the cycle retention and 4D high-temperature storage retention of coin cell full-cells were tested. The capacity and first-time efficiency testing process is as follows: 0.1 C charge-discharge test is performed using coin cell half-cells. The test process is as follows: constant current charging at 0.1 C to 1.5 V, then constant voltage charging to the cutoff current of 0.05 C, and resting for 10 min; constant current discharging at 0.1 C to 0.005 V, and resting for 10 min; where capacity is the first discharge capacity (mAh / g), and first-time efficiency (%) is the percentage value of the first discharge capacity to the first charge capacity.

[0068] The cycle retention rate test process is as follows: The coin cell battery is placed in a constant temperature test room at 25℃ and subjected to 100 charge-discharge cycles at a rate of 0.1 C. Specifically, it is charged to 4.3V using a constant current of 0.1 C, then charged to the cutoff current of 0.05 C using a constant voltage, and left to stand for 10 minutes; then discharged to 3V using a constant current of 0.1 C, and left to stand for 10 minutes. The discharge capacity of each cycle is recorded, and the percentage of the discharge capacity after 100cls of charge-discharge cycle test to the discharge capacity of the first charge-discharge cycle is used as the cycle retention rate (%) after 100cls. The high-temperature storage test process is as follows: The button cell is placed in a constant temperature test room at 25°C, and the first charge-discharge test is completed under the conditions of a voltage range of 3.0-4.3V and a test current of 0.1C. The battery that has completed the first charge-discharge test is stored at a high temperature of 60°C for 4 days (4D), and then the charge-discharge capacity of the battery is tested again under the conditions of a voltage range of 3.0-4.3V and a test current of 0.1C. The percentage value of the discharge capacity after storage to the discharge capacity before storage is calculated as the 4D high-temperature storage retention rate (%).

[0069] The results of the above tests are shown in Table 1 below.

[0070] Table 1

[0071] The results above show that silicon-carbon materials modified with soft carbon precursors can effectively reduce the proportion of surface silicon, resulting in lower gas production per unit time. They have significant advantages in terms of capacity, first-efficiency performance, and cycle performance. At the same time, reducing the proportion of surface silicon can effectively reduce interfacial side reactions, thus significantly increasing the retention rate of high-temperature storage.

[0072] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A method for producing a silicon-carbon composite material, characterized by, The method comprises: obtaining porous carbon; coating the porous carbon with a soft carbon precursor to obtain porous carbon with a coating layer, wherein the soft carbon precursor has a molecular diameter MD> 5 nm; carbonizing the coating layer to obtain carbonized porous carbon; depositing a silicon source on the carbonized porous carbon to obtain a silicon-carbon composite material.

2. The production method according to claim 1, characterized by, 5 nm < MD of the soft carbon precursor ≤ 200 nm; and / or, the mass of the soft carbon precursor is 5%-15% of the mass of the porous carbon; and / or the specific surface area of the porous carbon is 1500-2500 m 2 / g, and the pore volume is 0.6-1.2 cm 3 / g; and / or, the porous carbon is biomass-based porous carbon, including one or more of coconut shell carbon, bamboo charcoal or rice husk carbon; and / or, the solvent includes one or more of toluene, hexane, tetrahydrofuran; and / or, the soft carbon precursor includes one or more of aqueous asphalt emulsion, polyvinyl chloride, polyacrylonitrile, chitosan or starch derivatives.

3. The production method according to claim 1 or 2, characterized by, The soft carbon precursor and the porous carbon are respectively mixed with a solvent to form a soft carbon precursor solution and a porous carbon dispersion liquid, and then the soft carbon precursor solution and the porous carbon dispersion liquid are mixed and coated.

4. The production method according to any one of claims 1 to 3, characterized by, In the step of carbonizing the coating layer, the inert atmosphere is nitrogen or argon, the temperature of the heat treatment is 800-2000°C, and the time of the heat treatment is 1-4 h.

5. The method of any one of claims 1-4, wherein, The silicon source for the deposition of the silicon source is silane, and the temperature for the deposition of the silicon source is 400-600°C.

6. The method of any one of claims 1-5, wherein, The step of depositing the silicon source is followed by carbon source vapor deposition, wherein the carbon source for the carbon source vapor deposition is acetylene, methane or ethylene, and the deposition temperature is 400-600°C.

7. The preparation method according to claim 6, characterized in that, The silicon-carbon composite material is placed in a 0.1M potassium hydroxide or sodium hydroxide alkaline solution, and the gas production per unit mass G is < 10 ml / mg after 24 hours.

8. A silicon-carbon composite material, characterized by, The method is prepared by any one of claims 1-7.

9. A secondary battery characterized by comprising: The silicon-carbon composite material of claim 8.

10. Use of the silicon-carbon composite material of claim 8 in a negative electrode sheet, a secondary battery, and an electrical device.

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